This is an interesting question and one that is surely on the mind of just about every student debating an engineering career. However, the question really isn’t that appropriate. After all, if you are thinking about entering the engineering profession, then you really shouldn’t ask yourself what the easiest path is. That kind of thinking will only add to the 50% dropout rate amongst engineering students. Look, if you are doing it right, school will be challenging and rewarding, regardless of the specific degree. Pursue what you find interesting and you will find that the course work is “easy” for you.
With that disclaimer in mind, I thought I’d see what the general consensus was for the “most difficult engineering discipline”. There are a few great threads on the matter going on here, here, and here. According to the commenter’s, it would appear that Chemical and Computer/Electrical engineering get the “most difficult” prize (with a polite nod towards the rocket scientists and the biomeds). For that to be true, we would expect that the total number of Chem/Comp engineers to be far less that than the other major branches (they are). We would also expect the Chem/Comp graduates to earn more than the other major branches (they tend to).
Thus, one should probably assume that Chem/Comp is one of the more difficult paths to pursue if you aren’t particularly geeked about the subject matter. But, really, this could be said about any of the majors at a competitive school (architecture was dubbed archiTORTURE on my beloved campus, but the students actually doing the work seemed to love it).
So what to make of all of this?
You need to think critically about what kind of engineering type activities you like to do (coding, working on cars, writing, research, etc.) and then pick a branch that will get you there. Can’t decide? Then consider taking the Mechanical Engineering path. ME’s are widely considered to be “utilitarian” engineers, meaning that they can be plugged into any organization, in pretty much any role, and get they job done. Plus, the fundamental thing you learn in any engineering discipline is how to think. Get good at doing that and you will find yourself employable for the rest of your career. With an ME degree, you can go anywhere (but you may not make the most money).
For me, the bottom line is simple: Follow your passion, do what you love. If you are chasing the money, or chasing the easiest path, then you will usually end up disappointed.